The present invention relates to valves in general and more particularly, to a ported gate valve for use in slurry service.
Ported slide gate valves are usually used in slurry service because these valves provide good wear resistance to abrasive slurries. Ported slide gate valves with rubber or elastomeric seats that allow tight shut-off provide the most efficient type of valve performance in these harsh environments. The rubber or elastomeric seats also serve as wear resistant liners for the valve interiors. Such a valve conventionally utilizes a gate with an aperture and an operator that opens or closes the gate in one motion.
Some slurry systems generate a hard scale in the pipelines and valve interior surfaces. In those environments, operators are typically configured with larger than normal operating forces so that the opening or closing of the gate breaks the hard scale build up.
However, when such a valve closes, the gate typically drags the scale fragments into the seats, thereby tearing them. This tearing destroys the valve seats and consequently, results in premature valve failure.
Prior art systems occasionally used metal seats for such valves, in order to avoid seat damage. However, metal seated valves do not provide as tight of a shut-off as rubber or elastomeric seated valves.
Therefore, a need exists for a ported slide gate valve which overcomes the problem of scale build up and also enables the utilization of rubber or elastomeric seats with such a valve. Eliminating those problems would improve overall valve performance, prolong valve life and reduce maintenance and downtime costs.
The present invention relates to a ported slide gate valve where the gate has an open position, in which a portion of the gate having an aperture is aligned between ported elements to allow the passage of fluid through the valve, and a closed position, in which a solid portion of the gate is aligned between the ported elements. A means is coupled to the gate so that, prior to the movement of the gate to the closed position, the gate first has a reverse movement in a direction counter to the closing direction. This reverse movement breaks any scale buildup on a seat or seats, located in the valve interior, in such a manner that the scale is broken in a direction away from the seat or seats and deposited in the fluid.
Another aspect of the invention includes having a primary piston and a secondary piston as part of the means for moving the gate, where the primary piston is coupled to the gate in order to cause the movement of the gate. In the valve open position, the secondary piston holds the primary piston in the desired position. A movement of the secondary piston causes the reverse movement to break the scale.